*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
    background-color: #000;
}
a{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    width: 400px;
    height: 120px;
    color: #fff;
    text-align: center;
    line-height: 120px;
    font-size: 48px;
    text-transform: uppercase;
    text-decoration: none;
    font-family: sans-serif;
    background: linear-gradient(90deg,#03a9f4,#f441a5,#ffeb3b,#03a9f4);
    background-size: 400%;
    border-radius: 30px;
    z-index: 1;
}
a:hover{
    animation: animate 8s linear infinite;
}
@keyframes animate {
    0%{
        background-position: 0%;
    }
    100%{
        background-position: 400%;
    }

}
a::after{
    content: "";
    position: absolute;
    top: -5px;
    left: -5px;
    right: -5px;
    bottom: -5px;
    z-index: -1;
    background: linear-gradient(90deg,#03a9f4,#f441a5,#ffeb3b,#03a9f4);
    background-size: 400%;
    border-radius: 40px;
    opacity: 0;
    transition: 0.5s;
}
a:hover:after{
    filter: blur(20px);
    opacity: 1;
    animation: animate 8s linear infinite;
}

